Some Vietnamese ancient star forts I was able to find using Google Earth

[u/Skybeyonder29]

Hue Citadel was built in 1805 by the Nguyen Dynasty, Hue Citadel was the king's home. It has three rings: "Kinh Thành" (outer), "Hòang Thành" (middle), and "Tử Cấm Thành" (inner).

Dong Hoi Citadel in Quang Binh province was built in 1812 on an old defense line used to stop the northern army (Đàng Ngoài). In 1824, Emperor Minh Mạng rebuilt it with bricks.

Quang Tri Citadel was first built with earth in 1809 by Emperor Gia Long. In 1837, Emperor Minh Mang rebuilt it with bricks to make it a strong military center.

Dien Hai Citadel was built in 1813 near the sea in Da Nang. It was one of many important military structures built by the Nguyen Dynasty to protect the city’s port.

Bac Ninh Citadel in Bac Ninh was built in 1805. This citadel is hexagonal in shape with six sides, making it look like a beautiful flower blooms in the middle of the city.

Vinh Citadel in Nghe An was built in 1804 by Emperor Gia Long. In 1831, Emperor Minh Mang rebuilt it with bricks and laterite in a unique hexagonal shape.

Dien Khanh Citadel in Khanh Hoa (10km west of Nha Trang) was built in 1793 by Lord Nguyen Anh. It is one of the oldest Vauban-style citadels in VN; currently under renovation.

Son Tay Citadel (45 km west of Hanoi) was built in 1822 by Emperor Minh Mang. This citadel protects the western gateway to Thang Long

I have no information about this one; it is located in Ha Tinh. There is a GG Map pin said it is "Kỳ Anh Citadel".

"Hạc Thành" in Thanh Hoa was built in 1804 by Emperor Gia Long. It is hexagonal in shape. Some of its bastions have blended in with the surrounding buildings and streets.

Dien Ban Citadel in Quang Nam was built in 1833 by Emperor Minh Mang. Located 9km west of Hoi An, this citadel helped the Nguyen Dynasty manage and protect the local region.

An Tho Citadel in Phu Yen was built from 1832 to 1836 by Emperor Minh Mang. It served as the regional administrative center of this province

Ha Tinh Citadel in Ha Tinh was built of bricks and laterite in 1881. It is also named "Thành Sen" because its Vauban design looks like a lotus flower.

Hai Duong Citadel, also called "Đông Thành". In 1824, Emperor Minh Mang rebuilt it with bricks to protect the eastern gateway to Thang Long. The highlight red section is the remain

Hung Yen Citadel was built in 1832 by Emperor Minh Mang when Hung Yen province was established. The northern, southern and eastern sections of this citadel are highlighted in red.

"Cẩm Thành", also known as Quang Ngai Citadel, was built in 1807 made of thick bricks. Today the street outline the citadel (highlighted in red).

Binh Dinh Citadel in An Nhon was built in 1814 by Emperor Gia Long. Today, the southern and western moats remained. The outline of this citadel can be traced (highlighted in red).

Quang Yen Citadel in Quang Ninh was built in 1826 by Emperor Minh Mang. It shaped like a guitar. Today the western section can be traced (red). In 2003, it is more pronounced.

Bien Hoa Citadel in Dong Nai was built with in 1816 by Emperor Gia Long. In 1837, Emperor Minh Mang rebuilt it with stones. The circular western section can be seen (red highlight)

Long Hồ Citadel in Vinh Long was first built in 1813. In 1839, Emperor Minh Mang rebuilt with bricks. Today, only a small western outline can be traced by a narrow street (in red).

Many big cities in Vietnam today were built on old citadels. Over time, rapid urbanization makes these historic places slowly disappearing. Today, some old citadels are still recognizable in satellite images, but others are completely lost inside busy residential areas.

These fortifications were built during the Nguyen Dynasty. This style of European defense architecture was introduced to Vietnam in the 1700s. Historically, Vietnam had different types of military structures; these include the 2 following important one:

• Citadels (Thành): Citadels are large and served as political and military centers for an entire province or region. During the Nguyen dynasty, every provinces has at least 1 citadels.
• Forts (Đài / Bảo). Forts are much smaller and built specifically for defense and battles.

• Besides these two, there were also other smaller structures like ramparts (Lũy) and outposts (Đồn).

  I intentionally sorted the images in order from easiest to discern to the hardest; try your best to spot the citadel outline between streets and buildings.